1. Field of the Invention
The present invention relates to a linear or free piston compressor, particularly but not solely for use in refrigerators.
2. Summary of the Prior Art
The inventions disclosed in the present application relate to linear compressors and free piston machines. There are numerous examples of linear compressors and free piston machines in the prior art. A recent example is described in our international publication WO 02/35093. Our refrigeration compressor is described in that publication. The compressor includes a piston assembly reciprocal within a cylinder assembly. The piston assembly and cylinder assembly are connected by a main spring at a tail end of each assembly. A linear electric motor has a stator positioned between the cylinder and the main spring and an armature positioned between the piston and the main spring (on a connecting piston rod). The linear electric motor is energised to drive the compressor at a resonant frequency as required. The compressor is adapted for oil free operation, with gas bearings operating between the piston and cylinder walls and supplied with a compressed refrigerant from the cylinder head. The disclosure of WO 02/35093 is incorporated herein by reference, and is summarised at the beginning of the detailed description of the present application to place the present inventions in their preferred context.
However many of the present inventions are also applicable in other compressor configurations.
Our international publication WO 01/29444 shows a compressor configuration where the linear electric motor is provided concentrically with the piston and cylinder. In many other respects that compressor is similar to the compressor in WO 02/35093. U.S. Pat. No. 5,525,845, assigned to Sun Power Inc also describes an oil free linear compressor using gas bearings where the linear electric motor is provided concentric with the piston and cylinder, and a range of other configurations as well.
U.S. Pat. No. 6,089,352, assigned to LG Electronics Inc, describes a linear compressor where the linear electric motor is provided concentrically with the piston and cylinder. Oil lubrication is provided rather than gas bearings.
U.S. Pat. No. 4,416,594, assigned to Sawafuji Electric Company Limited, describes a linear compressor which uses oil lubrication. The armature of the linear electric motor surrounds the stator. A suction valve is provided in the piston head so that refrigerant for compression enters the compression space through the piston rather than through the cylinder head. Other examples which include suction through the piston head are shown in WO 00/32934, assigned to Matsushita Refrigeration Company and U.S. Pat. No. 3,143,281, by H Dölz.
All of the above are examples of resonant compressors including a spring between a piston part and a cylinder part. This arrangement is typical of linear compressors for refrigerant compression such as might be used in an air conditioner or domestic appliance. Other prior art linear compressors are known which do not make use of such a spring connection. Typically these compressors are used in Stirling cycle cryogenic coolers where the refrigerant gas is alternately compressed and expanded within the same locale. U.S. Pat. No. 5,146,124 and U.S. Pat. No. 4,644,851, both assigned to Helix Technology Corporation, are both examples of such an arrangement.